Technical Field
The invention relates to wide-angle lenses, having high quality images across the entire field of view in a compact form factor.
Related Background Art
Digital imaging cameras use solid-state image sensors such as CCD or CMOS imagers to convert optical images into electronic signals. As the resolution of the imagers increases, there is a continuous need for optical lenses with increased performance. An important characteristic of the lens is the ability to produce high-resolution images across a wide field of view. Another important characteristic is to produce such high-resolution images using a lens that is of a compact size. The lenses are increasing being incorporated into a variety of electronic devices including mobile phones, cameras, sports cameras, computers and computer peripherals. Incorporation of the lenses into new devices also places new environmental performance requirements upon the lens. The lens must be compact and light, to be used in portable devices, and must maintain high performance characteristics.
The quality and pixel density of very small imaging sensors is continuously improving. The sensors are used in machine vision, medical, cell phone and automotive applications. In many cases low distortion is critical to proper functioning in the intended application. These lenses are being used more and more in consumer application where literally millions of such lens systems must be easily produced at consistent high quality and at low cost. Custom lens features required to produce low distortion must be designed such that they are also easy to manufacture.
Lateral chromatic aberration is the separation of image height on the focal plane at off-axis field points between light rays of different wavelengths. This aberration becomes more significant and difficult to correct for wide-angle lenses. Similarly optical distortion is separation of image features on the focal plane at off-axis field points resulting in distortion of shapes and inconsistency of image feature detail location across the image plane.
Both types distortion cannot be fully corrected through mathematical manipulation of the digital images, in order for such corrections to be effective requires that the lens designer produces a well behaved lens. Optical distortion aka fisheye distortion is a departure from f-tan condition (where the image height is equal to the product of the effective focal length and tangent of the field angle). A distortion free lens would follow the f-tan relationship perfectly. Optical distortion is more difficult with wide angle lens that are designed to be compact.
There is a need for new lens designs that exhibit low color aberration and low optical distortion that follow the f-tan relationship and the lens is a compact lens.
There is a need for new lens designs that exhibit low color aberration and low optical distortion that follow the f-tan relationship, especially for wide-angle (field of view greater than 80o) and super wide-angle lens designs (field of view greater than 170o).
There is also need to provide super wide-angle and fisheye lens designs that can be manufactured cheaply, consistently and can be automatically assembled.